Gaseous fueled internal combustion engines are one way to reduce oil consumption and reduce engine emissions. Gaseous fueled engines may provide several advantages over liquid fuels such as gasoline or alcohol. For example, gaseous fuels vaporize well at low temperatures. Further, gaseous fuels may combust more completely because the fuel does not condense in the engine before combustion. Therefore, gaseous fuels may produce fewer undesirable emissions during some conditions.
However, the present inventors have determined that it may be difficult to start a gaseous fueled engine at low temperatures because fuel injectors resist movement at lower temperatures and because vehicle voltage may drop to a level where it may be difficult to operate the gaseous fuel injector. In particular, as engine cranking torque increases, the engine speed and battery voltage are reduced. For example, during engine cranking, a starter rotates the crankshaft of an engine. While the crankshaft rotates, engine cylinders induct and exhaust air for combining with fuel so as to provide a combustible mixture with which to operate the engine. During crankshaft rotation, air enters a cylinder during an intake stroke and is compressed during a compression stroke. The engine starter torque increases as the cylinder piston approached top dead center of the compression stroke because work is required to compress the air in the cylinder. Further, motor torque is directly proportional to motor current. As starter torque increases, the battery supplies increased current, and the battery voltage is reduced. If the battery voltage goes below a minimum operating voltage for the gaseous fuel injector, the fuel injector may not operate and the engine may not start.
In addition, it should be noted that although some types of fuel injectors may produce more fuel injector opening force at lower temperatures (e.g., peak and hold fuel injectors—fuel injectors that are actuated at a higher voltage and held open at a lower voltage), this type of fuel injector may require more expensive electronic driver technology. Therefore, peak and hold fuel injectors may be less desirable. Further, peak and hold fuel injectors are used less frequently as port injectors as saturating injectors are being developed that have lower minimum operating voltage. However, saturating fuel injectors have not been developed that operate at low minimum operating voltage that may be experienced at low temperatures.
The inventors herein have developed a method for injecting fuel to an engine, comprising: during an engine start in a first mode, adjusting injection timing of a gaseous fuel injector to deliver at least a portion of gaseous fuel to a cylinder of an engine during different crankshaft intervals; and aligning an opening of said gaseous fuel injector to a crankshaft angle where a supply voltage of said gaseous fuel injector exceeds a threshold voltage.
Engine cold starting of a gaseous fueled engine can be improved by adjusting start of injection timing (e.g., the crankshaft angle at which a fuel injector is commanded to begin to deliver fuel to an engine during a cylinder cycle) to coincide with a time during which voltage supplied to a fuel injector is at a higher level. By starting fuel injection at a time when voltage applied to a fuel injector is higher, the possibility of the fuel injector operating and injecting fuel can increase. For example, for a single cylinder engine, battery voltage can increase while a starter is engaged during an expansion stroke of a cylinder. During an expansion stroke, the compressed cylinder gases expand to accelerate the crankshaft and lower current drawn by the starter. Therefore, it may be beneficial during some conditions to actuate a gaseous fuel injector during an expansion stroke of a cylinder or at another crankshaft interval when voltage supplied to a fuel injector is higher. In this way, lower cost saturation type fuel injectors may be operated such that gaseous fuel is delivered to the engine even when battery voltage is not as high as is desirable. In the case of a multi-cylinder engine, the gas torques of all cylinders are superimposed to yield a net gas torque. The region of minimum gas torque may yield the fastest crank speed, the lowest starter current, and the highest battery voltage.
In the case of a four cylinder, four-stroke cycle, even firing engine, the higher battery voltage and lower battery voltage portion of the engine cranking cycle repeats every 180 crankshaft degrees. Thus, the crankshaft angular region or window when the battery voltage exceeds the minimum injector operating voltage can be determined every 180 crankshaft degrees.
The present description may provide several advantages. Specifically, the approach may improve engine starting and emissions. Further, the method can reduce system cost because a peak and hold circuitry is not required to operate the gaseous fuel injector. Further still, the vehicle power system may not have to be upgraded to operate fuel injectors during cold conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.